The invention relates to optical detection, and more particularly to optical detection systems and methods using interferometric detection.
Diagnostic tests based on a binding event between members of an analyte-ligand binding pair are widely used in medical, veterinary, agricultural, manufacturing and research applications. Typically, such methods are used to detect the presence or amount of an analyte in a sample, and/or the rate of binding of the analyte to the ligand. Examples of analyte-ligand pairs include complementary strands of nucleic acids, antigen-antibody pairs, and ligand-ligand binding agent, where the analyte can be either a member of the pair, the ligand molecule, or the opposite member.
Diagnostics methods of this type often employ a solid surface on which ligand molecules are immobilized, to which sample analyte molecules bind with high specificity and varied affinities at a defined detection zone. In this type of assay, known as a solid-phase assay, the solid surface is exposed to the sample under conditions that promote analyte binding to immobilized ligand molecules. The binding event can be detected directly, e.g. by a change in the mass, reflectivity, thickness, color or other characteristics indicative of a binding event. Where the analyte is pre-labeled, e.g., with a chromophore, or fluorescent or radiolabel, the binding event is detectable by the presence and/or amount of detectable label at the detection zone. Alternatively, the analyte can be labeled after it is bound at the detection zone, e.g., with a secondary, fluorescent-labeled ligand antibody.
Application of interferometry, for example, as an optical sensor, is challenging when it is being used in an industrial environment due to the high amount of perturbations in industrial environments. For example, in an interferometric measurement, it is desirable for the optical components to be in a vibration free and temperature stabilized environment. The cavity length is critical, because interferometric fringes require a stable optical path to create stable fringes. In some cases, the laser wavelength may shift over the length of the exposure. Although short exposure times (few seconds or less) may reduce the amount of wavelength shift, short exposure times may not always yield desirable results. For example, in the case of holography, short exposure times may not suit the type of holography that is desired.
Typically, transmission loss, reflection loss, or fringe shift is calculated for these types of sensors to account for environmental perturbations (such as vibrations, and temperature changes). When a monochromatic radiation source is employed, then transmission loss, reflection loss, or fringe shift is calculated. However, in the case of a broadband source, it is additionally required to track the spacing of the different wavelengths.
The sensitivity of the sensor depends on the precision with which the changes (transmission loss, reflection loss, or fringe shift) can be tracked. The precision or sensitivity may depend on the optical or electronic noise in the system.
Ideally, it would be desirable to stop everything on the benchtop from resonating, creeping, shrinking, distorting, buckling, flowing, rocking, sinking, expanding, bowing, settling, slipping or waving in the breeze (such as fan breeze). However, this is rarely possible.
Therefore, it is desirable to have an improved optical sensing device with stable path length regardless of the environmental perturbations.